**Core Concept:** Herpes zoster is caused by the reactivation of the varicella-zoster virus, which initially infects the dorsal root ganglia (DRG) during chickenpox. In herpes zoster ophthalmicus, the most affected nerves are the ophthalmic branches of the trigeminal nerve (V1), followed by the maxillary nerve (V2) and then the mandibular nerve (V3).

**Why the Correct Answer is Right:** In herpes zoster ophthalmicus, the least involved nerve is typically the abducens nerve (CN VI). The abducens nerve is part of the cranial nerves and is responsible for lateral eye movement (abduction). It is less frequently affected due to its location within the skull and its lesser contact with the virus in comparison to the trigeminal and ophthalmic branches of the trigeminal nerve.

**Why Each Wrong Option is Incorrect:**

A. Facial nerve (CN VII): This nerve is incorrect because it is part of the trigeminal nerve (CN V) and is more commonly affected in herpes zoster ophthalmicus due to its involvement in facial sensation and movement.

B. Oculomotor nerve (CN III): This nerve is incorrect because it is part of the trigeminal nerve (CN V) and is more commonly affected in herpes zoster ophthalmicus.

C. Trochlear nerve (CN IV): This nerve is incorrect because it is part of the trigeminal nerve (CN V) and is more commonly affected in herpes zoster ophthalmicus.

D. Accessory nerve (CN XI): This nerve is incorrect because it is not directly involved in the trigeminal nerve (CN V) and does not contribute to the ophthalmic region, making it less likely to be affected.

**Clinical Pearl:** Understanding the anatomy and pathophysiology of herpes zoster ophthalmicus is essential for proper diagnosis and management of the condition. A knowledge of the distribution of the cranial nerves can help differentiate between herpes zoster ophthalmicus and other ocular disorders.